The present invention relates to an external rotor motor, especially for driving fans, including a stationarily arranged inside stator as well as an outside rotor arranged to turn about the inside stator. The stator-lamination pack of the inside stator is provided with a central bore into which there is installed, with the aid of a clamp seating, a stator bushing which is joined mechanically on one side with the motor flange carrying the external rotor motor. Inside the stator bushing, there is a turnable shaft which is fixedly secured on the side lying opposite the motor flange, within a rotor bushing of the turnable outside rotor.
For the driving of small fans, which are used, for example, for the ventilating of electric tools, frequently external rotor motors are equipped with an inside stator, as well as an outside rotor arranged to turn about this inside stator. The main reason for the use of such external rotor motors in conjunction with small or compact fans is that the fan blades can be provided by welding or pressing a fan wheel onto the rotor, or by pressing a plastic fan wheel provided with a hood onto the rotor, so that the production of the fan is simplified.
In the construction of such external rotor motors, the outside rotor is borne turnably with respect to the stationarily arranged inside stator, for which purpose the stator lamination pack of the inside stator is provided with a central bore through which there is slid a shaft which is fastened on one side to the bell-shaped outside rotor. For the bearing of the rotor shaft inside the bore of the stator lamination pack, there are provided, as a rule, two ball bearings spaced from one another, inside a bearing tube that is pressed into the bore of the stator lamination pack. The bearing tube is used, furthermore, for the establishment of the mechanical connection between the stationary inside stator and an outer motor flange, to provide the mechanical suspension of the external rotor motor.
In view of this additional function of the bearing tube, it is extended into a portion of the motor flange, the face surface of the bearing tube forming a stop surface which lies on the motor flange. The connection between the bearing tube of the inside stator and the lateral rotor flange can occur either with the aid of a single central screw (see German patent No. 21 02 679) or with the aid of several peripherally arranged screws (see German published application AS No. 25 60 207), it being necessary in the first case for the bearing tube to be provided with an inside thread, and in the second case with an outside flange.
From German unexamined patent specification OS No. 32 23 057, there is known a detachable holding arrangement for a bearing. This holding device serves for the reception of the bearing of the shaft. The corresponding part of the casing has a base with a hole for the passage of the shaft. The bearing member, here a ball bearing, is held on the base of the casing part by means of an upset metal plate which grips over the bearing member. For the fastening of the metal plate to the base, there are provided holding projections and centering projections on the base of the casing which interact with corresponding parts of the plate, which on turning, lead to the fastening of the bearing.